overdrive trans question

I'm asking for a friend so I'll give you all the info he gave me.

Vehicle is a

78 dodge d150
318
2 wheel drive
Automatic
Regular cab
8ft bed

And heres his question

I want to replace the 727 with a good overdrive like the 518? (i think that's it) any suggestions on this? I need something non computer controlled and strong enough not to blow up if I'm hauling a bed of mulch or drywall lol. The build purpose of this truck is to use it as a truck and to cruise...my days of racing are done with...i just want better gas mileage and reliability.

I am absolutely clueless on this, and the only thing that popped in my head was "If you could just put a different factory trans in place of a 727 why would so many people buy gear vendors overdrives?

So any help is appreciated.

518 swap should be pretty easy in a 2-wheel drive truck.

No OD info but in the meantime you might dial in the dist & possibly go leaner or richer depending on where the carb is at now & the most restrictive system is the exhaust. You might put in a new timing chain & adv it 4 deg. a 360 MIGHT give better mileage. what is the axle ratio?

Well, I have a stick shift, but I'll say this - 0.75:1 accomplishes little improvement and is a waste of time and money to convert. What is worthwhile is 0.5:1.

Here's what I mean. Top photo is direct drive 1:1 at 60 mph, 2,750 rpm

Next photo is 0.75:1 at 60 mph, 2,300 rpm, a savings of 450 rpm. Meh.

Bottom photo is 0.5:1 at 60 mph, 1,550 rpm, a savings of 1,200 rpm. Perfect.

This is what you get in the cockpit in real life, not what the math says it ought to be.

518 is 0.69, 80mph @ 2500rpm, 3.73 gears
Math is spot on..........

Here's a good read, covers everything you need to know about 518 swap,
Hardest part for you will be modifying the cross member.

http://www.cuda-challenger.com/cc/index.php?topic=84774.0

Since you mention gas mileage and reliability, there are 2 other options:

1. a833od manual. I have a few of these and they are awesome.
2. 318 Magnum + it's transmission + all the factory computer stuff. Nothing beats tapping the key on a Magnum and having it light up right away compared to these Carter-carbed POS 318's.


Or, for what the cost and time involved to do this, you can pick up a 2nd gen for $1500.00

I'm doing this swap right now for my '77 440 D200 and have posts about this. Read the current one about my 518 reverse drum problem. If you choose to do it, find an early 90s(46RH).

Sometimes when the RPM is too low, it lugs the engine and actually gets worse mileage than slightly higher RPM. The O/P has a 318 truck and may not like too much OD reduction.

Gotta agree with Grizzly, swapping in a 318-360 magnum and trans will do exactly what is needed and provide a lot more 'comfort'.
Turn the key and go.
Craigslist is full of wrecked 94-up 1500's and there are now several sources for the wiring.

Classic example is the Viper; 3.08 axle ratio with .5 OD in 6th gear. You gotta be doing 85 mph to use 6th and then the throttle is like mush.

I like this swap and with a lock up converter it's even better.

I would suggest a trans no earlier than a 92 model though as they had the larger cooler lines which lubes the rear clutch drum and O/D unit.

Stay with a 95 or older unit as they are not electronic like the 96 and newer which will require a trans controller. 95 and back you can use two toggle switches, one each for the od and lockup. Some people have rigged up ways to operate them so they are a more automatically done shift to od/lu otherwise if you don't have a way to switch the new features it will just shift right in to od/lu when you are hardly moving. Some of the earlier units were od only and ran a standard non lu converter. Trans Go had instructions in their shift kits to modify the lube passages in the earlier units to prevent lack of lube issues that were a problem on some transmissions. If you run the numbers down, some applications had a more hd trans than others with features like more frictions discs, stouter planetary assemblies etc. The best v8 units were behind the 5.9's aka 360's. Even better for internals were the v10 and cummins units if you are going for the gusto. Since the 95 and older units were hydraulic, shift kits were easier and make more of an improvement which will help trans life. Another cheap and sometimes free improvement for the 97 and older units is to get a pan off the 98 and newer trans which is deeper and adds 2qts to you fluid capacity. You can find them at the diesel specialty shops or trans shops when someone puts a deeper aluminum pan on their cummins trucks. Do this for the regular 727's also but for them you need a filter extension.

At the end of the day, it's tough to win with any Dodge overdrive auto from 1988 to 2003.

The 545rfe is the best thing that ever happened and WHY nobody can make one to work with a Magnum/LA I'll never know.

At the end of the day? What about early morning driving?